In the absence of family pedigrees, measures of average inbreeding in a population are usually based on the excess of homozygotes at a single locus over that expected under Hardy-Weinberg assumptions. However, these estimates are not precise because of their high sampling variances. The average inbreeding can be more precisely measured by jointly observing the homozygosity and heterozygosity at several loci in each individual of a given population. Since inbred individuals have an increased probability of being homozygous at every locus, multi-locus inbreeding coefficients should provide a basis for partitioning departures in homozygosity into that due to consanguinity and that due to other forces which may affect each locus differently. The accuracy of this partition can be tested using immunogenetic and biochemical markers in populations of non-human primates. The availability of populations of pedigreed rhesus monkeys at the Wisconsin Regional Primate Research Center is a unique resource for measuring inbreeding both from pedigree data (consanguineous matings) and from multi-locus immunogenetic data analyzed by the methods we propose to develop.